Testing of payload-carrying network fibers with an OTDR (“live fiber testing”) is a recent application, mainly driven by Passive Optical Networks (PON). Not all networks are designed to handle out-of-band testing and there is a risk that out-of-band OTDR light pulses (e.g. at wavelengths above 1600 nm) damage network transceivers. Aside from live fiber testing, there may be circumstances where OTDR acquisitions are launched into fiber links connected to a network transceiver such as an SFP (Small Form-factor Pluggable) transceiver. There is then a risk that a network transceiver be damaged by in-band or out-of-band OTDR light pulses. When troubleshooting such fiber links, some OTDR users may have to resort to guessing as to OTDR acquisition conditions that will not damage the transceivers.
Typically, transmitters can be very robust against OTDR pulses compared to receivers. Under normal conditions, a transmitter will not be damaged by an OTDR pulse. On the receiver side, it was found that although pulse widths of 5 or 10 ns are generally safe in normal operation of state-of-the-art OTDRs, failures may occur with pulses as short as 30 ns. The problem is that such short pulses often offer insufficient dynamic range for link troubleshooting.
There is therefore a need for OTDR measurements with a safe mode that would be both safe for transceivers and allow fault finding within a fiber link.